The present invention relates to techniques for drying particulate matter in a fluidized bed process. More particularly, the present invention relates to an apparatus and method for drying a hygroscopic absorbant in a fluidized bed followed by treatment of a second material with the dried absorbant in the same vessel. The invention is yet more particularly directed to an apparatus and method for drying alumina in a fluidized bed and subsequently passing a monomer through the dried alumina for absorbing unwanted materials (e.g., methacrylic acid) from the monomer prior to using the monomer for manufacturing an ophthalmic lens such as a contact or intraocular lens.
Drying of particulate matter utilizing a fluidized bed process is known. See, for example, the following U.S. patents:
U.S. Pat. No. 3,889,388 issued to Takeda Chemical Industries, Ltd. On Jun. 17, 1975
U.S. Pat. No. 4,170,074 issued to Owens-Illinois, Inc. on Oct. 9, 1979.
In both the above patents, the apparatus for drying the particulate matter has no other purpose than to simply dry the particulate matter. Thus, once the particulate matter has been dried in the apparatus, the dried matter is removed from the apparatus for use in a separate processing station of the applicable manufacturing operation employed. In the ""388 patent, the particulate matter is foodstuffs and the apparatus is directed toward drying and breaking up agglomerates of the particulate matter without harming the structure of the particles themselves. There is no discussion as to subsequent processing steps which utilize the dried particulate matter, however, since the particulate matter disclosed is foodstuffs, it is more than likely that the particulate matter is at least part of the final product of the manufacturing process (e.g., a vitamin tablet, see Col. 1, Ins. 1-24 therein).
In the ""074 patent, the apparatus is similarly used for drying and breaking up of agglomerates of the particulate matter where the particulate matter is subsequently applied to a preheated work piece (e.g., glass bottle) via electrostatic application. Thus, the particulate matter being treated is also part of the finished product of the manufacturing operation.
In particular manufacturing operations, it is often necessary to use an absorbing agent to remove unwanted components from another material where the material being so treated is part of the final product of the manufacturing operation. For ease of description, the material being treated will be referred to as the xe2x80x9cproduct materialxe2x80x9d and the absorbing agent will be referred to as simply as xe2x80x9cabsorbantxe2x80x9d hereinafter, although it is understood that the invention is not limited to the type of materials being used with the present invention. The absorbant, which is by definition hygroscopic, will draw moisture from the environment when exposed thereto. Thus, if the manufacturing operation allows the absorbant to be exposed to the environment prior to it being used to treat the product material, the absorbant will not be at the most optimum dryness level at the time it is used to treat the product material. The prior art drying apparatus simply do not address this particular manufacturing process issue.
It would therefore be desirable to have an apparatus which dries the absorbant immediately prior to treating the product material with the absorbant. It would furthermore be beneficial to be able to both dry the absorbant and treat the product material in the same vessel. As such, the absorbant will be at its optimum dryness when used for treating the product material.
The present invention provides an apparatus and method for drying a particulate material that is used for treating a product material which has not heretofore been addressed in the prior art. The apparatus comprises a vessel into which a particulate absorbant is added for drying using a fluidized bed process where a dry gas (e.g., dry air or nitrogen) is delivered into the vessel from the bottom to create a fluidized bed of the absorbant which effectuates the drying process. Once the appropriate level of dryness is achieved and the absorbant has cooled, the product material is delivered into the vessel and forced through the dried absorbant material which removes unwanted components from the product material. The purified product material is then removed from the vessel through a conduit to a collection vessel located exteriorly of the drying vessel. In the most preferred embodiment, the vessel is kept airtight during the product material treatment stage to prevent any moisture from being reabsorbed into the absorbant. As such, the absorbant is at its most efficient dryness stage prior to treating the product material.